The invention relates to a drive circuit for an electric motor having an aerodynamic bearing of the motor shaft.
Air bearings are bearings in which two parts moving against one another are separated by a thin air film. They thereby allow an almost friction-free relative movement.
The air bearing can in particular be used with electric motors in which the driven motor shaft, i.e. the rotor, is supported by an air gap in the motor housing. A distinction is made between static bearings and dynamic bearings in air bearings. With static bearings, the air gap is generated by introduction of compressed air by external means. Dynamic bearings do not require any compressed air supply since the compressed air required in the air gap is generated by inherent movement. The problem arises here, however, that the two bearing parts which move with respect to one another can contact one another below a characteristic relative speed and are thus subject to wear and increased friction.
Air bearing motors are used, for example, in air-conditioning units, in particular in air-conditioning units for rail vehicles. The air bearing motors are coupled to a compressor and drive it. Since the air-conditioning system, like other consumers within the rail vehicle, are fed by the supply voltage of the overhead line, this voltage supply can be briefly interrupted at specific transition points. Depending on the interruption period, this can have the result that the speed of the air bearing motors in air-conditioning units is abruptly reduced, down to a standstill, and sufficient compressed air for the air bearing cannot be generated. Harmful friction phenomena thereby arise within the air bearings and the service life of the motor is greatly reduced.